Field
Embodiments of the invention relate to the field of force transmissions; and more specifically, to force transmissions for use in surgical instruments intended for use in minimally invasive surgeries.
Background
Minimally invasive surgery (MIS) (e.g., endoscopy, laparoscopy, thoracoscopy, cystoscopy, and the like) allows a patient to be operated upon through small incisions by using elongated surgical instruments introduced to an internal surgical site. Generally, a cannula is inserted through the incision to provide an access port for the surgical instruments. The surgical site often comprises a body cavity, such as the patient's abdomen. The body cavity may optionally be distended using a clear fluid such as an insufflation gas. In traditional minimally invasive surgery, the surgeon manipulates the tissues by using hand-actuated end effectors of the elongated surgical instruments while viewing the surgical site on a video monitor.
The elongated surgical instruments will generally have an end effector in the form of a surgical tool such as a forceps, a scissors, a clamp, a needle grasper, or the like at one end of an elongate tube. The surgical tool is generally coupled to the elongate tube by one or more articulated sections to control the position and/or orientation of the surgical tool. An actuator that provides the actuating forces to control the articulated section is coupled to the other end of the elongate tube. A means of coupling the actuator forces to the articulated section runs through the elongate tube. The actuator may control an articulated section, such as a “wrist” the orients and manipulates the surgical tool, with means for coupling the actuator forces running through the elongate tube.
It may desirable that the elongate tube be somewhat flexible to allow the surgical instrument to adapt to the geometry of the surgical access path. In some cases, the articulated sections provide access to a surgical site that is not directly in line with the surgical access port. It may be desirable to use cables as the means of coupling the actuator forces to the articulated sections because of the flexibility they provide and because of the ability of a cable to transmit a significant force, a substantial distance, through a small cross-section. However, a cable is generally only able to transmit a force in tension. Thus it is generally necessary to provide two cables to transmit a bidirectional actuating force. The articulated section may be in the form of a gimbal that provides angular motion with two degrees of freedom around a center of rotation. A gimbal can be controlled by three cables.
If a wrist is to be provided with a wide range of motion, for example ±90°, it may be desirable to stack two gimbal joints and provide half of the motion in each of the two joints. This provides a more gradual change of direction at the wrist which may be advantageous if cables have to pass through the wrist to control the end effector. The two stacked sets of joints can be made to create a constant velocity joint that avoids the singularity or gimbal lock that occurs at 90° with one set of joints. It requires six cables to control two stacked gimbal joints. However, the six cables do not have independent motions.
In view of the above, it is desirable to provide an improved apparatus and method for transmitting actuating forces through an elongate tube of a surgical instrument intended for use in minimally invasive surgeries that uses six cables connected to two stacked gimbal type articulated sections.